North Hawaii News Articles from CFHT

Volcanos Everywhere!

Every resident of the Big Island knows there is an active volcano very near them. There are other volcanos on Earth too (about 800 are active or dormant); but did you know that there are volcanos on other planets and satellites?

A volcano is a vent (crack, hole, any aperture) in a planet's (or a satellite's) crust from which hot molten rock, steam, water, dust, ashes, and gasses are ejected. Hot springs and geysers also are manifestations of volcanic activity, resulting from the interaction of ground water with magma.

Volcanos have a few causes. On Earth, the most common cause is movement of tectonic plates; those plates are sections of the terrestrial crust that float freely on a layer of molten rock. When they collide with one another or are spread apart, lava flows from the cracks. The other volcanos on Earth (about 5%) appear above hot spots (like the Hawaiian volcanos). Elsewhere in our Solar System, giant impacts of comets or asteroids can break the crust of planets or satellites and release lava.

Space probes have detected the remnants of ancient volcanic eruptions on the Moon, the red planet Mars, and Mercury. Triton (a satellite of Neptune), Io (a satellite of Jupiter), and Venus are the only bodies in the solar system besides Earth that are known to be volcanically active right now. Recently, Europa, another of Jupiter's satellites, has been found to show evidence of volcanic activity.

Those eruptions are of rocky material and are driven by internal heat, except on Io, Triton and Europa. On Io, the eruptions are probably of sulfur compounds and driven by tidal interactions with Jupiter and its other major satellites. On Triton, the eruptions are of very volatile compounds, such as methane or nitrogen, driven by seasonal heating from the sun. On Europa, what comes out is probably water.

Mercury is the closest planet to our Sun. It looks very similar to the Moon. Both show a heavily cratered and very old terrain, and regions of relatively smooth and younger plains. When you watch the Moon, you can easily see these two types of terrain: the young and smooth maria (or lunar sea) appear darker.

The Moon's maria are huge impact craters that were later flooded by molten lava.

On Mercury, some of the plains may be the result of ancient volcanic activity, but some may be deposits of dirt ejected from craters created by impacts. A recent reanalysis of Mariner 10 data revealed some evidence of volcanic activity on Mercury, such as signs of lava flows and deposits from explosive volcanic eruptions.

Ancient volcanic activity is also seen on Mars. Mars is known to have the largest volcano in the Solar System, Olympus Mons. (The largest volcano on Earth is our Mauna Loa, which is 9 kilometers (6 miles) high from its base, and 120 kilometers (75 miles) across).

This Mars volcano is 550 km (340 miles) across, three times higher than Earth's highest mountain (about 27 km (17 miles) tall - compare with Mount Everest which is about 10 km high) and has a volume over fifty times greater than Earth's largest volcano. The caldera at the top is over 70 km (45 miles) wide, and surrounding the volcano is a cliff that ranges up to 10 km in height!

The low gravity on Mars allows such huge structures as large as Olympus Mons to form. But Olympus Mons is not the only volcano; there is Alba Patera, with a base diameter of 1,500 kilometers (930 miles); Ceraunius Tholus, one of the smaller volcanos, but still about the size of the Big Island; Apollinaris Patera which rises only 5 km (3 miles) or so above the red surface, and many others.

Besides Earth, Venus, Io and Triton are the only places where we know volcanic activity is taking place now.

Venus, the second planet from the Sun, has been visited by over 20 unmanned spacecrafts. Most of its surface consists of plains with little relief, but radar imaging (a technique able to see through the thick clouds of Venus), has revealed the presence of lava flows on much of the surface, along with lava channels, cones, domes, and several large shield volcanos, such as the 8 km high Maat Mons, Gula Mons, and Sif Mons. Venus also shows interesting and unique features including pancake volcanos (eruptions of very thick lava) and coronae (collapsed domes over large magma chambers). Venus is still volcanically active, but only in a few hot spots.

Io is slightly larger than Earth's Moon and is the closest large satellite to Jupiter. Its surface is continually changing due to many powerful volcanos. Hundreds of volcanic calderas have been photographed. This activity is thought to be caused by Jupiter and its more distant Galilean Moons (Europa, Ganymede, and Callisto). Constantly pulling on Io and distorting its shape (by as much as 100 meters), they help generate internal frictional heating which in turn causes the eruptions. Photographs sent by Voyager in 1979, and more recently by Galileo, show ongoing eruptions that eject yellowish lava, probably made of sulfur or molten silicate rock. Sometimes, the eruptive plumes are 300 km (190 miles) high! Io's most prominent volcano is called Pele, after the Hawaiian fire goddess.

Europa, another Galilean Moon of Jupiter, presents a smooth icy surface interrupted by ridges, which may result from volcanic cracks in the ice where emerging liquid water freezes upon exposure to the cold of deep space. This is called cryovolcanism, a process related to eruption of ice and gases in geyser-like activity which shoots gas and rocky debris from Europa's interior.

Let's skip over the ringed Saturn and pale blue Uranus, to get to Neptune, the outermost gaseous giant. Triton is its biggest moon, and almost everything we know about it comes from the only spacecraft which has passed near Triton, Voyager 2, in 1989. Voyager found a very thin atmosphere, extensive ridges, valleys criss-crossing the surface in complex patterns, and, most interesting and totally unexpected, evidence for ice volcanos. The eruptive material is probably liquid nitrogen, dust, or methane compounds from beneath the surface. One of Voyager's images shows an actual plume rising 8 km (5 miles) above the surface and extending 140 km (86 miles) to one side.

To learn more about our Solar System, there are excellent Web sites that cover every aspect of each of the planets and satellites of our Solar System:

Nadine Manset
Resident Astronomer
Canada-France-Hawaii Telescope
Dec. 21, 2000